Maximum Voltage Drop 5%
Key to Longer Wire Runs
The Wiring Distance Chart gives the maximum length of a given remote lamp circuit, assume the entire remote load is concentrated at the end of the wire run. If remote lamp fixtures are uniformly spaced along the circuit path (equal watts spaced at equal distance), the lengths in the table may be increased, based on the chart and formula below:
# OF FIXTURES
For example, a 100-foot long, 12-volt, remote lamp circuit has four 12-watt fixtures spaced 25 feet apart. According to the Wire Distance Chart, #8 Ga. wire would be required for 48 total watts up to 112 feet, to allow a 5% voltage drop or less. However, since the fixtures are equal in wattage and are spaced equally along the circuit, the distance of 70 feet for #10 Ga. wire can be multiplied by 1.6 (70 x 1.6 = 112), so in this case up to a 112-foot wire run with #10 Ga. wire would be acceptable.
Note: For systems operating at less than 50 volts, the smallest permissible wire size is #12 Ga. copper or equivalent per NFPA70 (National Electrical Code), Article 720-4.